MOLLUSCA. 491 



giiiella, Cancellaria, Mitra, Ancilla, Volvaria, and Torna- 

 tella. The last genus contains the Valuta tornatilis of Bri- 

 tish writers. 



2. Shell turreted. The whorls of the shell, the revolv- 

 ing spire of which is subconical, scarcely embrace one an- 

 other, but are merely united at the margins. Three fami- 

 lies may here be established. 



Family 1. Buccintdiz. Canal short, scarcely produced 

 beyond the anterior margin of the lip, and bent towards the 

 right. The tentacula are remote, and the head is destitute 

 of a hood. The mouth has a retractile proboscis. The fol- 

 lowing genera belong to this family : Buccinum, Eburna, 

 Dolium, Harpa, Nassa, Purpura, Cassis, Morio, and Te- 

 rebra. 



Family 2. Muriceda. Canal produced, and straight. 

 The tentacula approach the head and mouth as in the 

 preceding family. The genera are Murex, Typhis, Ranella, 

 Fusus, Pleurotoma, Pyrula, Fasci olaria, and Turbinella. 



Family 3. Cerithiada. Canal short and recurved. Head 

 with a hood. This family contains the marine genus Ceri- 

 thium, and the fluviatile one Potamidum. 



Family 4. Strombusidee. Canal short, and bent towards 

 the right. The outer margin of the aperture becomes pal- 

 mated with age, and exhibits a second canal, generally near 

 the former, for the passage of the head. The following are 

 the genera : Strombus, Pterocera, and Rostellaria. 



2d Tribe. 



Shell internal. 



This tribe consists at present of only one genus, termed 

 Sigaretus, two species of which are natives of Biitain. The 

 foot of the animals belonging to this genus, or rather of the 

 species which constitutes the type, is oval, with a duplica- 

 ture in front. The cloak is broad, with an indentation on 



